1. Field of the Invention
The present invention relates to a communication control apparatus, a communication control method, a node, and a communication system. More particularly, it relates to an autonomous distributed communication control method for use in a communication system with nodes arranged in a grid.
2. Description of the Related Art
Known methods by which a plurality of spatially distributed nodes can transmit data without collisions include time division multiple access (TDMA) and carrier sense multiple access (CSMA), the latter including carrier sense multiple access with collision avoidance (CSMA/CA) and carrier sense multiple access with collision detection (CSMA/CD). A discussion of these methods can be found in, for example, Waiyaresu LAN Akitekucha (Wireless LAN Architecture), edited by Matsushita and Nakagawa, Kyoritsu Shuppan, 1996, pp. 47, 53-59, and 69 (in Japanese).
A weakness of the TDMA system is that if the central administrative node that assigns time slots malfunctions, the entire communication system may be brought down. Various collision avoidance methods in which the individual nodes adjust their time-slot assignments autonomously, without the need for a central administrative server, have therefore been proposed, as in Japanese Patent Applications No. 2003-328530, No. 2004-257562, and No. 2004-257567. In these proposed methods, each node interacts with its neighboring nodes by transmitting impulse signals at regular intervals and adjusting the timing of these intervals according to the timing of the impulse signals received from the neighboring nodes, using a nonlinear model that forces the transmission timing away from the receiving timing. A group of interacting nodes can thereby establish non-overlapping time slots in which to transmit data without collisions.
A plurality of nodes can be spatially distributed in many ways, one of which is a grid. When nodes are distributed in a grid pattern, in theory there is an optimal time-division communication mode in which the time slots of mutually adjacent nodes fit together in a non-overlapping pattern with very little lost time, resulting in highly efficient communication. When the above methods of autonomous time-slot assignment are applied to a grid of nodes, however, the nodes are unable to achieve this ideal mode of time-division communication and are therefore unable to reach the ideal level of communication efficiency.
It would therefore be desirable to have a communication control apparatus and method, a node, and a communication system in which a plurality of nodes arranged in a grid can autonomously adjust their data transmission timing to achieve high communication efficiency without requiring timing instructions from a central administrative server.